Fix a simple mistake that make native JSON.parse never been used

[aptx4869]

window.JSON.parse === 'function'

should be

typeof window.JSON.parse === 'function'

[gkatsev]

That's a pretty silly mistake. Thanks!

[aptx4869]

This mistake is simple but it breaks our app...
We use a CSP that call to eval is not allowed but Javascript JSON implementation use eval...

[gkatsev]

We're hoping that in a newer version of videojs, we're just going to remove this file altogether and make a valid JSON implementation a dependency. There's a bug related to that somewhere.

[heff]

Ha, wow. Thanks!

[heff]

Merged in, thanks!